How do I enable the “multiverse” repository? Please specify how to do this graphically and via command line.

The Multiverse repository contains software which has been classified as non-free. This software may not be permitted in some jurisdictions. When installing each package from this repository, you should verify that the laws of your country permit you to use it. Also, this software may not include security updates.

Command line

Uncomment (remove the # from the front of) the multiverse lines or add them in if needed, so the lines look like this:

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team, and may not be under a free licence. Please satisfy yourself as to
## your rights to use the software. Also, please note that software in
## multiverse WILL NOT receive any review or updates from the Ubuntu
## security team.
deb http://us.archive.ubuntu.com/ubuntu/ oneiric multiverse
#deb-src http://us.archive.ubuntu.com/ubuntu/ oneiric multiverse
deb http://us.archive.ubuntu.com/ubuntu/ oneiric-updates multiverse
#deb-src http://us.archive.ubuntu.com/ubuntu/ oneiric-updates multiverse

Uncomment the deb-src lines if you need to download the source code (most users will not need the source code, so if in doubt, leave them disabled).

Save your edit (if you are using nano, Ctrl+X , then type Y to save your changes) then, to update you r package list, run